Construction of fixed partial dental prosthesis



B. WEISSMAN CONSTRUCTION OF FIXED PARTIAL DENTAL PROSTHESIS June 17, 1969 Sheet Filed Nov. 9, 1965 B. WEISSMAN June 17, 1969 CONSTRUCTION OF FIXED PARTIAL DENTAL PROSTHESIS Sheet 2 orz Filed Nov. 9, 1965 United States Patent 3,449,830 CONSTRUCTION OF FIXED PARTIAL DENTAL PROSTHESIS Bernard Weissman, 304 Ashland Place, Brooklyn, N.Y. 11217 Filed Nov. 9, 1965, Ser. No. 507,072 Int. Cl. A61c 13/10 US. Cl. 326 4 Claims ABSTRACT OF THE DISCLOSURE A method of construction of a fixed dental prosthesis involving preparing the concerned teeth with bores, disposing a locating pin in each bore, forming in impression and disposing the head portion of the locating pin in the complementary cavities formed in the impression, reproducing a dental stone model from the impression wherein the pins are retained, forming a wax pattern of the prosthesis wherein the locating pin heads extend through the wax pattern, investing the pattern and model to form a metal casting of the desired prosthesis, removing the pins from the metal casting, positioning the metal castings on the involved teeth and securing the same in place by means of screw anchors extending through the apertures and in threaded engagement with the dentin of each tooth.

This invention relates to dentistry and more particularly, to a method for the construction of fixed partial dental prosthesis or bridges as well as to apparatus particularly adapted for the practice of the method.

It is an object of this invention to provide a simple, efficient and effective method for the construction and securement of fixed dental prosthesis or bridges with a minimum amount or reduction of the tooth structure or discomfort to the patient.

It is also an object of this invention to provide a method and means therefor whereby a fixed dental bridge may be formed in a manner to provide maximum retention and support in relation to the natural teeth of the patient as well as [for pontics and the like used for replacement of missing natural teeth.

It is also an object of this invention to provide means which facilitate and insure the successful practice of the instant method with a maximum amount of safety and comfort to the patient.

Other and further objects, benefits and advantages of the instant invention will appear from this specification and drawings as well as the claims appended hereto.

In the accompanying drawings:

FIGURE 1 is a lingual view of a group of teeth to which a fixed bridge and pontic link have been secured in accordance with the instant invention;

FIGURE 2 is a lingual view of a natural tooth in the process of preparation for the reception in accordance with the present invention;

FIGURE 3 is a labial-lingual cross-section of an anterior tooth, such as is shown in FIGURE 2, in the process of preparation taken along line 33 thereof:

FIGURE 4 is a view similar to FIGURE 3 showing a subsequent step in the preparation of the tooth showing a locating pin in pisition;

FIGURE 5 is an enlarged fragmentary view of a portion of the tooth shown in FIGURE 4 showing the relationship of the locating pin to the pin-receiving bore;

FIGURE 6 is an enlarged cross-sectional view of a rubber or similar impression having a locating pin reinserted therein;

FIGURE 7 is a view of a cast showing the locating pin channels and pins in the process of insertion;

3,449,830 Patented June 17, 1969 FIGURE 8 is a view of the cast to which the wax pattern of the bridge has been applied;

FIGURE 9 is a cross sectional view of FIGURE 8 taken along line 99 thereof;

FIGURE 10 is a cross sectional view of the cast metal. bridge as it is removed from the investment with the locating pin still in place;

FIGURE 11 is a cross sectional view showing the cast bridge with the pins dissolved out therefrom;

FIGURE 12 is a cross sectional view of a tooth similar to FIGURE 3 showing the tooth in the process of being redrilled;

FIGURE 13 and 14 are views similar to FIGURE 12 showing steps in the process of mounting the bridge; and

FIGURE 15 is a labial view partly in section showing the bridge in position on the teeth.

FIGURE 1 illustrates one of the many forms of fixed dental prosthesis or bridges in the construction of which the instant invention may be practiced with considerable advantage. Said figure illustrates the natural teeth 10, 11 and 12 to which the fixed bridge designated generally by the numeral 13 has been attached. The bridge 13 in addition to reinforcing the natural tooth structure, also illustrates the practice of the present invention in connection with a replacement for a missing tooth or pontic 14 which is suspended between the natural teeth.

As shown in FIGURES 2, 3, 4 and 5, the initial preparation of each of the natural teeth comprises the removal of portions of the incisal or occlusal surfaces, as the case may be, of the teeth to be treated. The reduction of the natural tooth structure may be extended along the lingual surfaces of the teeth and approaches the gingiva without contact therewith. It should be noted that the tooth preparation will vary with the location of the desired prosthesis. Thus, in the case of posterior teeth, the preparation may be limited to the occlusal surfaces while in the case of anterior teeth, portions of the lingual surfaces may be removed. The reduction or removal Olf the tooth surface is in the amount required for the thickness of gold in the area of the proposed bridge structure. Removal of the tooth structure in this manner is indicated by the numeral 15 in FIGURE 3, wherein the broken line 16 indicates the original tooth formation along the lingual surface of the tooth 12 for example. The enamel surface 18 of the tooth has thus been removed in this area together with some dentin 19.

With the aid of precise X-rays, the pulp location is charted in each tooth and the site and orientation of the bores 17 is charted so that they enter the dentin 19 without penetrating the region of the pulp 20, one such bore being illustrated in FIGURE 3. As an initial step, the area of the bore mouth is indented to form a countersunk bore mouth as indicated by the numeral 21. For this purpose, a burr provided with .a spherical bead, as indicated at 22, is advantageously employed.

The bore 17 is then drilled with its axis disposed in the charted orientation and to the prescribed depth. For this purpose, the use of a spiral drill 23 having a diameter of .024 inch is particularly advantageous. There is thus formed an appropriately oriented bore, the mouth of which is enlarged or countersunk by means of the indentation 21, the peripheral wall of which forms an abutment or reference surface for the locating pin 24.

As may be more particularly seen from FIGURES 4 and 5, locating pin 24 comprises a body portion or shaft 25 which preferably terminates in a hemispherical head. The shaft diameter is slightly smaller than the diameter of the bore, the difference being just suflicient to permit easy insertion of the shaft into the bore without introducing undesired play. With the bore hole formed by means of an .024-inch spiral drill, a shaft diameter of .023 inch accomplishes this purpose. The distal end of the pin 24 is provided with an enlarged head 26 which is advantageously .060 inch in diameter as well as an intermediate collar portion 27 which is advantageously .031 inch in diameter. A tapered transition portion 28 connects the head 26 with intermediate collar 27. At the juncture of the other end of collar 27 with shaft 25, a step or shoulder 29 is formed. This shoulder permits a planar reference surface disposed in a plane normal to the axis of the shaft. The length of the shaft portion of the pin 24 is selected so that the shaft end does not bottom in the channel. As a consequence of this, the planar surface of shoulder 29 will rest against the periph eral surface of the countersunk or indented mouth of the bore at all times. It will be noted that the diameter of the indentation 21 is substantially larger than the diameter of collar 27. The positioning pin 24 is preferably formed of nickel silver.

The bores 17 are purposefully oriented so that their axes are disposed in non-parallel direction as indicated in FIGURES 2 and 7 and a number of such bores are formed in the body of each tooth. A locating pin 24 is now disposed in each of the bores, it being apparent that the intermediate collar and head ends of the pins 24 protrude from the bores. An impression such as is illustrated in FIGURE 6 is then taken of the involved teeth in a silicone rubber or similar resilient impression forming material 30. In the course of the removal of the cured impression 30 from the involved teeth, the non-parallel orientation of the pins prevents their removal therewith. However, the resilience of the impression material permits it to be removed while the locating pins remain in the tooth structure, without destroying the impression. After separation of the impression 30 from the involved teeth, the locating pins 24 are withdrawn from their position in the bores 17 of the teeth and are reinserted head first into their respective positions in the impression cavities theretofore formed by the pin heads. It will be noted that the correct orientation of the pins is thus retained. This re-insertion is made possible, in spite of the undercut formed by the transition portions of the pins by reason of the resilient flexure of the impressional material. FIGURE 6 illustrates a pin 24 re-inserted in its corresponding head cavity and extending into the cavity formed by the tooth body and showing the impression 30 upon an enlarged scale.

With the pins 24 re-inserted in the impression 30, a master cast or model of refractory material conventionally employed in mechanical destistry is poured. Upon hardening of the master cast, it is removed from the rubber impression, the locating pins remaining in place in the cast. FIGURE 7 illustrates the master cast 31 thus formed. At this time, a second or auxiliary cast or model of the same impression is also poured for later use in fabricating individual dies. The second or auxiliary cast or model, not shown, is used for indexing the intraocclusal distances and is also used for forming a wax up or pattern of the desired fixed bridge. The wax pattern includes a wax up of the desired pontic link as an integral part thereof. The wax pattern 32 which, as indicated, is initially prepared on the auxiliary model, is then transferred to the master cast 31 and is pressed into position over the protruding heads of the locating pins 24, as may be more particularly seen from FIGURE 8. The wax pattern is then appropriately sprued according to conventional practice, and invested together with the master cast while still positioned thereon. The pattern is then processed and cast in gold or other appropriate dental metal by the lost wax process as is well known in the art. The'cast metal bridge 33 and the pontic link forming part thereof is then removed from the investment. It will be noted that the locating pins remain in the metal cast as may be seen from FIGURE 10. The locating pins are then dissolved in nitric-acid so that the metal casting 33 forming the bridge is now provided with apertures 34 which correspond in conformation to the head and intermediate collar portions of the locating pins as may be seen from FIGURE 11. The metal casting 33 is then relocated upon the auxiliary model to which reference has been heretofore made, and it is finished in accordance with conventional practice.

The bridge is placed in position over the prepared areas of the teeth in the patients mouth as is shown in FIG- URE 12. It will be noted that the apertures 34 comprise negative reproductions of the locating pin heads 26, intermediate collar 27 and transition portions 28. These apertures 34 register with the bores 17 and act as guides as the bores 17 are redrilled or rebored in the next step of the process. It will be noted that the initial drilling of each bore had been accomplished by means of a drill bit of .024 inch in diameter. In redrilling the bores, it is somewhat enlarged by use of a burr or drill bit 35 of .027-inch diameter. The drill 35 is provided with a tapered transition portion 36 which corresponds to the transition portion 28 of the locating pin reproduced in apertures 34 of the bridge. As a consequence of this, it is possible to redrill each of bores 17 to a preselected depth, depending upon the length of the portion of the drill from its tip to the transition portion 36. In redrilling the bore, the apertures 34 are also redrilled and precise registration, alignment and orientation of the apertures in the bridge with the bores in the teeth is thus assured.

In securing the bridge 34 in position, an anchor rod designated generally by the numeral 37 is employed. Anchor rod 37 comprises a threaded body portion 38 and a generally cylindrical head portion 39. At the juncture of the body portion 38 with the head portion 39 a tapered transition portion 40 is provided. The head and transition portions of the anchor 37 are complementary to the corresponding portion of apertures 34 in the bridge. The tip of the threaded body of the anchor is beveled so that a self-threading action is provided as the anchor begins to enter the somewhat compressible dentin surrounding the tooth bore. The apertures in the bridge are dimensioned to permit the free passage of the pin therethrough. The free end of the head portion of the anchor rod is flatened as indicated at 41 so that it may be held and retained for rotation by means of wrench 42 used for driving the same as shown in FIGURE 13. The screw threaded length of the anchor rod is selected so that it will not bottom against the bottom of the bore when completely seated in the bridge aperture thus leaving a small space at this location. With the bridge in position and the apertures and bores redrilled as heretofore indicated, an anchoring rod 37 is screwed into each such location, the anchoring rod being of a diameter to form complementary threads in the dentin of the tooth only. The anchors serve to draw the bridge tightly against the tooth body as the transition portions 40 of the anchors come into seating engagement with the complementary portions of apertures 34 in the bridge. During this process, the entire bridge is fitted for such characteristics as adaptation, accuracy and inter occlusal distance. The bridge is then removed, cement is applied, and the bridge is replaced. Thereupon, the anchors are again screwed in by means of the wrench and the bridge is firmly and tightly seated. After the cement has been completely set, the protruding portions of the anchors are cut off and finished smooth with the configuration of the bridge surfaces and then polished. By means of the instant process, the bridge is securely and permanently fixed to the retaining teeth. The retention characteristics of the anchors is enhanced by the non-parallelism of the anchors in relation to each other in each tooth as well as the relationship established between those in different teeth. It will also be noted that provision is made for the suspension of pontics which are formed integrally with the bridge.

I claim:

1. A method of construction of a fixed dental prosthesis which comprises reducing the natural tooth surfaces in the amount of the thickness of the proposed prosthesis, forming a plurality of bores in the bodies of the involved teeth, the mouths of the bores being located in areas to be covered by the prosthesis, the mouth of eachof the bores being enlarged to form an indentation, disposing a removable locating pin in each of said bores each of the pins having a head portion extending outwardly of the tooth surface, forming an impression of the involved teeth and the extending head portions of the pins in a flexible impression forming material and disposing the head portions of the pins in the complementary cavities formed in the impression, reproducing a dental stone model from said impression wherein the pins are retained, forming a wax pattern of the desired prosthesis on said model wherein the locating pin heads extend through the wax pattern, investing said pattern and model forming a metal casting of the desired prosthesis therefrom removing the pins from the metal casting to expose complementary apertures formed in said casting by the presence of the pins, and positioning the metal casting on the involved natural teeth and securing the same in place by means of screw anchors extending through the apertures in the casting and in threaded engagement with the dentin of each tooth.

2. The method of construction of a fixed dental prosthesis which comprises reducing the natural tooth surfaces in the amount of the thickness of the proposed prosthesis, forming a plurality of bores in the bodies of the involved teeth, the mouths of the bores being located in areas to be covered by the prosthesis, disposing a removable locating pin in each of said bores each of the pins having a head portion extending outwardly of the tooth surface, forming an impression of the involved teeth and the extending head portions of the pins in a flexible impression forming material and disposing the head portions of the pins in the complementary cavities formed in the impression, reproducing a dental stone model from said impression wherein the pins are retained, forming a wax pattern of the desired prosthesis on said model wherein the locating pin heads extend through the wax pattern, investing said pattern and model forming a metal casting of the desired prosthesis therefrom removing the pins from the metal casting to expose complementary apertures formed in said casting by the presence of the pins, and positioning the metal casting on the involved natural teeth and securing the same in place by means of screw anchors extending through the apertures in the casting and in threaded engagement with the dentin of each tooth, screw anchors each comprising a rod having a threaded body portion and a generally cylindrical head portion, a tapered transition portion being formed at the juncture of said head portion with said body portion.

3. The method of construction of a fixed dental prosthesis which comprises reducing the natural tooth surfaces in the amount of the thickness of the proposed prothesis, forming a plurality of bores in the bodies of the involved teeth, the mouths of the bores being located in areas to be covered by the prosthesis, disposing a removable locating pin in each of said bores each of the pins having a head portion extending outwardly of the tooth surface, forming an impression of the involved teeth and the extending head portions of the pins in a flexible impression forming material and disposing the head portions of the pins in the complementary cavities formed in the impression, reproducing a dental stone model from said impression wherein the pins are retained, forming a wax pattern of the desired prosthesis on said model wherein the locating pin heads extend through the wax pattern, investing said pattern and model forming a metal casting of the desired prosthesis therefrom removing the pins from the metal casting to expose complementary apertures formed in said casting by the presence of the pins, and positioning the metal casting on the involved natural teeth and securing the same in place by means of screw anchors extending through the apertures in the casting and in threaded engagement with the dentin of each tooth, said prosthesis being provided with a plurality of unthreaded apertures each having a countersunk portion in one face of said prosthesis and a protuberance surrounding said aperture in the other face of said prosthesis, said protuberance being secured in a corresponding indentation surrounding the bore in the tooth.

4. A dental prosthesis adapted to be fixedly secured to natural teeth in the mouth said prosthesis comprising a bridge adapted to overlie portions of the natural teeth, said bridge being provided with a plurality of unthreaded apertures extending from one face to the opposing face thereof each of said apertures having a countersunk portion on one face thereof and being adapted to receive an anchoring device in abutting engagement with one face of said bridge and threadedly engaged within the registering bore of a natural tooth, the opposing surface of said bridge being provided with protuberances adapted to be received in complementary indentations formed in the surface of a natural tooth, whereby said bridge is secured against an abutting tooth surface, said anchoring device comprising a rod having a threaded body portion, a generally cylindrical head portion and a tapered transition portion formed at the juncture of said head portion with said body portion, said protuberances surround the apertures formed in said bridge.

References Cited UNITED STATES PATENTS 973,343 10/ 1910 Corcor-an 32-6 1,649,905 11/1927 Lasky 32-5 2,494,229 1/ 0 Collison.

No. 1, pp. 138l56 relied upon (January-February 1962).

ROBERT PESHOCK, Primary Examiner. 

